audio/moc: unbreak with ffmpeg 4.0

ffmpeg.c:996:34: error: use of undeclared identifier 'CODEC_CAP_TRUNCATED'

if (data->codec->capabilities & CODEC_CAP_TRUNCATED)
                                ^

ffmpeg.c:997:23: error: use of undeclared identifier 'CODEC_FLAG_TRUNCATED'

data->enc->flags |= CODEC_FLAG_TRUNCATED;
                    ^

ffmpeg.c:1028:34: error: use of undeclared identifier 'CODEC_CAP_DELAY'

if (data->codec->capabilities & CODEC_CAP_DELAY)
                                ^

PR: 227726
Obtained from: Greg V